Fast primality test for small numbers

I'm looking for a library (or just a program) with a fast primality test for 64-bit numbers. In particular I'd like something that's faster than Pari which I'm currently using. I do need it to be programmable, of course, since billions of tests need to be done.

Any ideas? Or is Pari essentially as fast as I can get?

I'm going to try to port my program to Mathematica to do a speed comparison, but in past tests Pari beats Mathematica soundly in number theory.